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Edexcel Jun 2014 Paper 1 Q21
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![Acceptable Answers Reject Question Number 21(a) Mark (The energy / enthalpy change that accompanies the formation of) one mole of a(n ionic) compound (1) ALLOW as alternative for compound: lattice /crystal / substance / solid / product / salt from (its) gaseous ions (1) IGNORE References to standard conditions or any incorrect standard conditions ALTERNATIVE RESPONSE If no mark(s) already awarded from above, can answer by giving:- energy change / enthalpy change per mole (1) (1) 2Na+(g) + O2(g)Na2O(s) NOTE If lattice energy of dissociation is given (e.g. energy required to break down 1 mol of an ionic lattice into its gaseous ions) max (1) for the 2nd scoring point gaseous ions energy required / energy needed / energy it takes from one mole of gaseous ions (no 2nd mark) from gaseous elements (no 2nd mark) 6CH0101 1406<br />
Question Number 21(b)(i) Acceptable Answers Reject Mark 2Na+(g) + O2-(g) C (or 2C) E E (or 2E) D D (or 2D) 2Na+(g) + O(g) + 2e- 2Na(g) + O(g) 2Na(g) + O2(g) 2Na(s) + O2(g) 2Na+(g) + O-(g) + e- Na2O(s) All seven letters correct (3) Five OR six letters correct (2) Three OR four letters correct (1) ALLOW Either D or 2D Either C or 2C ALLOW Correct numerical values (see question paper) may be given as an alternative to the correct letters 6CH0101 1406<br />
Question Number 21(b)(ii) FIRST, CHECK THE FINAL ANSWER Acceptable Answers Mark Reject 1088 (kJ mol1) scores (0) overall (as two errors) (+)1088 (kJ mol1) also scores (0) overall (as several errors) IF answer = 2520 (kJ mol1) then award (2) marks, with or without working Otherwise look for 414 = (2108) + 249 + (2496) + (141) + 790 ) + HLE OR HLE = 414[ (2108) + 249 + (2496) + (141) + 790 ] OR A correct expression using letters e.g. F = (2)D + E + (2)C + A + B + G (1) (=4142106) = 2520 (kJ mol1) (1) NOTE ALLOW for 1 mark: 1692 (wrong sign for 414) 1916 (2108 and 2496 not used for Na+) 2412 (2108 not used for Na+) 2024 (2496 not used for Na+) +2520 (wrong sign for final answer) 2802 (sign changed for 1st electron affinity of oxygen) 2395.5 (atomization of oxygen halved) NOTE Penalise incorrect units (e.g. kJ mol) ONCE only NO ECF from incorrect answers to (b)(i) 6CH0101 1406<br />
Mark MgS is larger than MgO S2 has a larger atomic radius than O2 Question Number *21(c) Acceptable Answers Reject ALLOW reverse argument where appropriate First mark MgO more exothermic (than MgS) IGNORE greater / higher / larger (1) Second mark S2 larger than O2 (1) Third mark Charges on O2 and S2 same OR Charges on (all) ions same OR S2 smaller charge density than O2 NOTE This mark is awarded if both formulae for the ions O2 and S2 are mentioned (1) Fourth mark O2 (forms) stronger (electrostatic) attractions (than S2) IGNORE just stronger (ionic) bonds (1) Penalise ONCE ONLY the use of the word atom(s) or molecule(s)/ use of formulae such as Mg O O2, etc. AND/OR Penalise ONCE ONLY use of words such as just magnesium (instead of magnesium ions/Mg2+) and/or just oxygen (instead of oxide ions/O2) Mark each point independently (Total for Question 21 = 11 marks) 6CH0101 1406<br />](https://learnah.org/wp-content/uploads/2018/08/June_2014_MS_-_Unit_1_Edexcel_Chemistry_A-level_21-0.jpg)
